1. Field of the Invention
The present invention relates to a dielectric antenna having a filter function, a dielectric antenna having a duplexer function, and a radio apparatus using these.
2. Description of the Related Art
A microstrip antenna and a dielectric antenna have been used as an antenna in the microwave band, especially one suitable for a small-scale radio apparatus.
Furthermore, in general a reception filter is provided in order to extract a desired frequency signal from received waves, and a transmission filter is used to transmit only the desired frequency signal as a transmission wave. An antenna in which such filters are provided in the antenna portion to enable the entire device to be miniaturized is disclosed in Japan Unexamined Patent Publication No. 8-181533.
The above described microstrip antenna having a filter function comprises a microstrip antenna, the microstrip antenna comprising a ground conductor and a microstrip conductor provided on a dielectric substrate. And a dielectric resonator is constituted on the dielectric substrate. By this arrangement, the microstrip antenna and the dielectric filter can be provided on a single dielectric substrate. However, since the antenna portion and the filter portion are independent of each other, transmitting means must be separately provided in order to input the receive signal to the filter portion, and loss occurs in this part. This causes deterioration in the electrical characteristics.